The present studies on the isolation and characterization of a vasoactive factor existing in plasma of certain patients with hypertension will be continued and extended. Present knowledge on the cause of hypertension cannot explain its etiology in the majority of patients on the basis of the renin-angiotensin system alone, since many of them have either normal or low renin activity levels. Similarly, the etiology of malignant hypertension and pregnancy induced hypertension remains incompletely understood. Our studies this far indicate that there is a vasoactive factor in the blood of such patients and in animals with experimental hypertension which potentiates the vascular sensitivity to pressor agents. This factor is not present in plasma of normotensive subjects. Our present studies indicate that this factor can be obtained only from plasma of hypertensive subjects using column chromatographic procedures and it is concentrated only in certain fractions. Our studies also suggest that this sensitizing factor is negatively charged at neutral pH and it could be a polypeptide or a small protein. We propose to do further studies on the isolation, purification, characterization and identification of this vasoactive factor utilizing various techniques including column chromatography, ion exchange procedures, eletrophoretic methods and tissue preparations. Following its isolation, characterization and identification, attempts will be made to synthesize it chemically and to develop antibody to it. This antibody will be used to develop a radioimmunoassay procedure which could be utilized in studies of hypertension. The isolation and characterization of such a factor will provide new knowledge which is essential for the elucidation of the etiology and mechanism of maintenance of hypertension. Such knowledge will lead to the design of specific inhibitors of vassopressor substances which in turn, may provide the basis and stimulus for the development of better means for the prevention and therapy of hypertension.